Electron sources are extremely important in electronic devices used in displays. Display devices include plasma and liquid crystal displays, as well as cathode ray tubes. Cathode ray tubes are bulky and consume a tremendous amount of power in electronic systems. Plasma displays are expensive, have low contrast, and are temperature dependent. Plasma displays also have poor resolution capabilities.
Electron field emitters are becoming increasingly popular for display devices. This is primarily due to the development of cheap and robust field emitters. Field emission involves the extraction of electrons from a solid by tunneling through the surface potential barrier. The emitted current depends directly on the local electric field at the emitting surface and on its work function. This process is typically called Fowler-Nordheim tunneling. Field emission devices typically use a structure commonly known as a Spindt tip for the emitter. However, Spindt tips require a very small size feature to provide the desired emission and control of the emitted electrons. This very small size is extremely difficult to achieve and these tips are prone to serious damage to the tip during high current emission or if it is not uniformly constructed. However, electron field emitters offer better resolution and generate less heat than other technologies currently available.
Nanotubes are one such field emitter that can potentially be used in display technology such as flat panel displays. Nanotubes are excellent electron sources, providing a stable current at very low electric fields and are capable of operating in moderate vacuum. Nanotubes also have low turn-on fields and high current densities.
However, nanotubes need to have uniform field emission over the entire area and need to be properly orientated to achieve useful current densities at low electric fields. Typically, as deposited nanotubes are randomly orientated and adhered in a binder or otherwise adhered to the surface at multiple locations along the length, which makes it impossible to achieve significant and uniform field emission. The field emission is improved by orientating the nanotubes so that one end is attached to the cathode of the device and the second end is pointed at the anode. This is called “activating” the nanotube and increases the likelihood that an emitted electron will reach the anode and subsequently produce an emission current.
Prior methods to reorientate or activate the nanotubes include mechanical brushing or polishing. However, physically contacting the nanotubes tends to spread them to unwanted areas, causing the current to be extracted from undesirable locations. Furthermore, post activation processes, such as wetting during a cleaning step, can cause the nanotubes to lose their orientation and become deactivated.
It would be highly advantageous, therefore, to remedy the foregoing and other deficiencies inherent in the prior art.
Accordingly, it is an object of the present invention to provide a new and improved nanotube field emission device and a method for fabricating such a device.
It is an object of the present invention to provide a new and improved nanotube field emission device with a method that allows the nanotubes to be orientated in a controllable manner.
It is a further object of the present invention to provide a new and improved nanotube field emission device with a method that allows the nanotubes to be orientated after device processing.
It is an object of the present invention to provide a new and improved nanotube field emission device with a method that allows the nanotubes to be orientated without making physical contact with the device structure.
It is another object of the present invention to provide a new and improved nanotube field emission device that requires less power to operate.
A further object of the invention is to provide a new and improved nanotube field emission device with a large field emission current.